This we have chemical nociceptors, thermal nociceptors,

This lesson will cover the basics of pain. We’ll discuss the different types of pain, the basic mechanism of pain, what structures are involved, and how your own body or drugs try to stop it.

Pain: A Four-Letter Word

In this lesson, we’re going to be discussing a four-letter word, but it’s probably not the one that you’re thinking of.

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The word we’ll be dealing with is something that is sometimes used to refer to our emotional, mental, or physical needs. This word is very negative. It can be short-lived or it can last a long time. It’s called pain. And it’s a really nasty four-letter word.

Nociception

The ability to sense pain is thanks to a process known as nociception.

More technically, nociception is the ability to sense noxious stimuli that in and of themselves can hurt you. While you may hate being in pain, it’s actually critical to your survival. Although proof for this is currently lacking for many different reasons, it’s likely that anything that is able to actively escape a predator is able to sense pain.

There would be little reason for something to actively move away from a source of potential harm other than the fear of pain, the fear of death, or both.The reason you should be grateful for pain lies well beyond just the evolutionary basics. For example, if you were burned by a hot stovetop and had no ability to sense pain, you’d also be less likely to either notice the burn or care to do anything about it. Since the throbbing pain wouldn’t be there to constantly warn you about the burn, you’d leave it alone, since the stovetop isn’t a predator out to kill you. However, this action, or inaction to be more precise, would still predispose your body to infection through the burn, which could then kill you. In essence, pain is your body’s alarm system that ends up saving your life.

In fact, a rare genetic condition where a person is unable to feel pain or react to it is known as congenital analgesia, and can cause significant harm to a person unaware of serious, normally pain-inducing, conditions that may be occurring in their body. Actually, in the movie The Girl Who Played with Fire and its sequel The Girl Who Kicked the Hornet’s Nest, that rare disorder accounted for why Lisbeth Salander’s gigantic half-brother couldn’t be hurt with any kick, throw, or Taser gun.

Types of Noxious Stimuli

With that in mind, there are three major types of noxious stimuli to which people with congenital analgesia are unable to sense or react to.

These include:

  • Mechanical noxious stimuli, such as pinching, tearing of the skin, and other physical deformations of the body’s structures that result in pain,
  • Thermal noxious stimuli – stimuli that cause pain through temperature extremes.
  • Chemical noxious stimuli – chemically based irritants, such as capsaicin, that induce pain sensation.

The nerves that sense noxious stimuli affecting the body are collectively known as nociceptors, and individually are known by the type of stimulus they respond to. Therefore, we have chemical nociceptors, thermal nociceptors, mechanical nociceptors, and so forth.

Pain’s Pathway through Our Body

Once any sensory nerve, the nociceptor, senses some kind of noxious stimuli, it gets really excited and sends an electrical signal to the spinal cord. At the spinal cord, the nociceptor meets, or synapses, with another nerve. At this junction, the nociceptor releases a neurotransmitter, such as glutamate or substance P, which then, in turn, activates the nerve cell the nociceptor has synapsed with. It’s easy to remember that substance P is involved in pain, since you can think of the P as representing the word pain.In any case, the nerve located in the spinal cord then sends a signal to the brain’s thalamus, which among other things is a structure in the brain involved in relaying and processing pain sensation. From here, the signal travels to the brain’s cerebral cortex, which is a higher-order structure involved in everything from memory to awareness.

The pain signal that travels to the brain may eventually cause the release of pleasure producing neurotransmitters, such as endorphins, a type of opioid. These endorphins are released thanks to structures such as the pituitary gland and hypothalamus, the structure in the brain that is responsible for maintaining your body’s homeostasis, or normal states of equilibrium. I like to think of the hypothalamus as Lady Justice. If she senses something is wrong or weighted too heavily to one side, she does something to the other side of the scale to even things out. In our case of pain, as soon as the brain signals to the hypothalamus that the body is in pain, it causes the release of opioids that produce pleasure and return the body’s sensations back to normal.

Once these endorphins are released into the body, they land on their appropriate receptors. These receptors, in the case of opioids, are unsurprisingly known as opioid receptors. Once an opioid lands on its receptor it essentially tells the body’s nerves to calm down and stop firing off signals about the pain they are sensing. To be more specific, one way they do this is by inhibiting the release of substance P, one of the things that allows nerves to signal pain in the first place. This is how pain relieving drugs, such as morphine, which in and of itself is an opioid, work to reduce pain in our body.

Other Types of Pain

Something to keep in mind is that with this description we’ve only barely scratched the surface of the complex nature of pain and the way by which it is controlled, sensed, and classified. For instance, pain doesn’t have to be stimulated only by temperature, chemicals, or mechanical factors. We can also experience pain when nerves are damaged, we are shocked with electricity, our stomach hurts, or we are emotionally hurt. Yes, believe it or not, many of the same things we learned about in this lesson are involved in emotional pain. Therefore, emotional pain isn’t fake pain, it’s just as real to your body neurologically and chemically speaking as pain caused by getting your fingers slammed in the door.

Lesson Summary

I hope, at the very least, this lesson didn’t cause you any undue pain and that you’ll experience some pleasure reviewing everything with me one more time. Recall that the ability to sense pain is thanks to a process known as nociception.

More technically, nociception is the ability to sense noxious stimuli that in and of themselves can hurt you.There are three major types of noxious stimuli to which people with congenital analgesia are unable to sense or react to. These include chemical, mechanical, and thermal noxious stimuli. The nerves that sense noxious stimuli affecting the body are collectively known as nociceptors, and individually are known by the type of stimulus they respond to.Once any sensory nerve, the nociceptor, senses some kind of noxious stimuli, it gets really excited and sends an electrical signal to the spinal cord. At the spinal cord, the nociceptor meets, or synapses, with another nerve. At this junction the nociceptor releases a neurotransmitter, such as glutamate or substance P, which then, in turn, activates the nerve cell the nociceptor has synapsed with.

It’s easy to remember that substance P is involved in pain, since you can think of the P as representing the word pain.In any case, the nerve located in the spinal cord then sends a signal to the brain’s thalamus, which among other things is a structure in the brain involved in relaying and processing pain sensation. The pain signal that travels to the brain may eventually cause the release of pleasure producing neurotransmitters, such as endorphins, a type of opioid. These endorphins are released thanks to structures such as the pituitary gland and hypothalamus, the structure in the brain that is responsible for maintaining your body’s homeostasis, or normal states of equilibrium.

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